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// Copyright 2016 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#include "draco/core/encoder_buffer.h"
#include <cstring> // for memcpy
#include "draco/core/varint_encoding.h"
namespace draco {
EncoderBuffer::EncoderBuffer()
: bit_encoder_reserved_bytes_(false), encode_bit_sequence_size_(false) {}
void EncoderBuffer::Clear() {
buffer_.clear();
bit_encoder_reserved_bytes_ = 0;
}
void EncoderBuffer::Resize(int64_t nbytes) { buffer_.resize(nbytes); }
bool EncoderBuffer::StartBitEncoding(int64_t required_bits, bool encode_size) {
if (bit_encoder_active()) {
return false; // Bit encoding mode already active.
}
if (required_bits <= 0) {
return false; // Invalid size.
}
encode_bit_sequence_size_ = encode_size;
const int64_t required_bytes = (required_bits + 7) / 8;
bit_encoder_reserved_bytes_ = required_bytes;
uint64_t buffer_start_size = buffer_.size();
if (encode_size) {
// Reserve memory for storing the encoded bit sequence size. It will be
// filled once the bit encoding ends.
buffer_start_size += sizeof(uint64_t);
}
// Resize buffer to fit the maximum size of encoded bit data.
buffer_.resize(buffer_start_size + required_bytes);
// Get the buffer data pointer for the bit encoder.
const char *const data = buffer_.data() + buffer_start_size;
bit_encoder_ =
std::unique_ptr<BitEncoder>(new BitEncoder(const_cast<char *>(data)));
return true;
}
void EncoderBuffer::EndBitEncoding() {
if (!bit_encoder_active()) {
return;
}
// Get the number of encoded bits and bytes (rounded up).
const uint64_t encoded_bits = bit_encoder_->Bits();
const uint64_t encoded_bytes = (encoded_bits + 7) / 8;
// Flush all cached bits that are not in the bit encoder's main buffer.
bit_encoder_->Flush(0);
// Encode size if needed.
if (encode_bit_sequence_size_) {
char *out_mem = const_cast<char *>(data() + size());
// Make the out_mem point to the memory reserved for storing the size.
out_mem = out_mem - (bit_encoder_reserved_bytes_ + sizeof(uint64_t));
EncoderBuffer var_size_buffer;
EncodeVarint(encoded_bytes, &var_size_buffer);
const uint32_t size_len = static_cast<uint32_t>(var_size_buffer.size());
char *const dst = out_mem + size_len;
const char *const src = out_mem + sizeof(uint64_t);
memmove(dst, src, encoded_bytes);
// Store the size of the encoded data.
memcpy(out_mem, var_size_buffer.data(), size_len);
// We need to account for the difference between the preallocated and actual
// storage needed for storing the encoded length. This will be used later to
// compute the correct size of |buffer_|.
bit_encoder_reserved_bytes_ += sizeof(uint64_t) - size_len;
}
// Resize the underlying buffer to match the number of encoded bits.
buffer_.resize(buffer_.size() - bit_encoder_reserved_bytes_ + encoded_bytes);
bit_encoder_reserved_bytes_ = 0;
}
} // namespace draco
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